Wellbores are typically drilled using a drilling string with a drill bit secured to the lower free end and then completed by positioning a casing string within the wellbore and cementing the casing string in position. The casing increases the integrity of the wellbore and provides a flow path between the surface and a selected subterranean formation for the injection of treating chemicals into the surrounding formation to stimulate production, for receiving the flow of hydrocarbons from the formation, and for permitting the introduction of fluids for reservoir management or disposal purposes.
During conventional milling and/or drilling operations, a casing window assembly may be used for completion of a lateral wellbore. A conventional casing window assembly generally includes a section of casing with a pre-milled window through the side of the casing for entry by a tool and an outer sleeve comprising aluminum connected around the pre-milled window to protect the annulus within the casing from debris and cement as the casing is secured within the wellbore. This type of casing window assembly, however, presents several disadvantages such as, for example, a larger outside diameter around the casing where the outer sleeve is connected, a lower pressure rating and it must be milled before drilling the lateral wellbore.
Other conventional casing window assembly designs include a section of casing with a pre-milled window through the side of the casing for entry by a tool and an inner steel sleeve connected to the pre-milled window to protect the inside of the casing from debris and cement as the casing is secured within the wellbore. Although this type of assembly provides a better seal for the pre-milled window and may have a higher pressure rating, it requires a separate trip to retrieve before drilling the lateral wellbore. This extra-separate trip to remove the inner sleeve can cost upwards of $100,000.00 to retrieve from a deep wellbore.
Other components of a conventional casing window assembly may include, for example, a mandrel for carrying a whipstock and/or a completion deflector and a separate orienting member secured below a pre-milled window in the casing for orienting the whipstock and/or the completion deflector at the proper lateral position and depth that is substantially the same lateral position and depth as the pre-milled window. The orienting member thus, orients the whipstock and/or completion deflector in order that the milling/drilling tool may enter the formation through the pre-milled window at the proper lateral position and depth. Because most conventional orienting members provide orientation both for a lateral position and depth at the same time, achieving a proper lateral position and depth in deeper wells can be time consuming and difficult due to the amount of torque imposed on the drilling string. In other words, as the drilling string is turned slowly from the top, the torque from turning the drilling string builds up and causes the bottom of the drilling string, where the whipstock and/or completion deflector are located, to turn rapidly in deeper applications. This often prevents finding the proper lateral position, which is not known until the torque is transmitted back up the drilling string.